Our rich diversity of life on Earth is the outcome of over three billion years of evolutionary history. It has been shaped by forces such as continental drift, ice ages, fire, weather, and the interaction of all the different species that inhabit the earth. Now, it is increasingly being altered by the dominant species of the planet, humans. From the dawn of agriculture over 10,000 years ago, through the industrial revolution of the past three centuries, the human species has reshaped Earth's landscapes on an ever-larger and lasting scale. Despite growing awareness and increasing investments in environmental protection, pressure on the world's natural resources and ecosystems continues to increase rapidly. The impacts of human activities envelop every aspect of the natural world. No ecosystem on Earth is free from pervasive human influence (World, 2006). Global warming, pollution, and the unabated use of the Earth's natural resources have given rise to questions of our planet's continued ability to sustain us. Global atmospheric changes, such as ozone depletion and climate change, only add to the stress. Global warming poses an extraordinary challenge. The world's leading scientists tell us that a gradual warming of our climate is under way and will continue. This long-term warming trend poses serious risk to the world's economy and to the environment. It poses even greater risks for poorer countries that are far less able to cope with a changing climate and for low-lying countries where a rise in sea level will cause significant damage. Meeting the challenges of global warming will require sustained effort over decades--on the part of governments, that must establish regulations and modify them as we learn more about climate change and as technological solutions begin to manifest themselves; on the part of industry, which must innovate, manufacture, and operate under a new paradigm where climate change will drive many decisions; and on the part of the citizens of the world, who must not only be educated on the effects of climate change but who must also switch to a more Earth-friendly path in purchases and lifestyles. While the earth has always undergone changes in its climate and environment, the potential importance of human contributions affecting changes on a global scale has emerged comparatively recently. Global public opinion, like American public opinion, has been most recently influenced by the unprecedented drought in Brazil, the melting Arctic ice, the recent hurricane season, and a torrent of scientific findings.
The Science of Climate Change
Global warming is shorthand for "climate change," and the term is correct if you realize that it's referring to the average temperature of the earth over the years; not the temperatures at particular times and places. Climate change is a much better term to use than global warming because much more than warming is involved, although the changes begin with the average temperature of the earth increasing. Studying past climates can help put the twentieth century warming into a broader context, lead to better understanding of the climate system, and improve projections of future climate temperatures.
Because widespread, reliable instrumental records are available only for the last 150 years or so, scientists must estimate climatic conditions in the more distant past by analyzing proxy evidence from sources such as tree rings, corals, ocean and lake sediments, cave deposits, ice cores, boreholes, glaciers, and documentary evidence. Starting in the late 1990s, scientists began combining proxy evidence from many different locations around the world in an effort to construct an estimate of surface temperature changes that have occurred over broad geographic regions during the last few hundred to few thousand years. Controversy arose because many people interpreted this result as definitive evidence of anthropogenic causes of recent climate change, while others criticized the methodologies and data that were used. …